Arrangement for an axial bearing in a drilling machine

ABSTRACT

The invention relates to an arrangement for an axial bearing in a drilling machine. The drilling machine includes a frame (6), a percussion device (1) fitted in the frame, and a shank (2) positioned on an axial extension of the percussion device. The frame (6) further includes an axial bearing formed by a number of pistons (4a, 4b) to receive axial forces acting on the frame (6) through the shank (2). The length of travel of some pistons (4b) towards the forward portion of the drilling machine is limited so that when they are in their forward position and the shank (2) is supported by the pistons (4a, 4b), the shank (2) is substantially at its optimal percussion point.

TECHNICAL FIELD BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an arrangement for an axial bearing in adrilling machine comprising a frame; a percussion device fitted in theframe; a shank positioned on an axial extension of the percussiondevice; means for rotating the shank; and an axial bearing fitted in theframe to receive axial forces acting on the frame through the shank, theaxial bearing being formed by several pistons accommodated in axialhousings formed in the frame along a periphery circumscribing the shankand interconnected with a conduit system, the pistons being furtherarranged to act on the shank so as to force it towards the forwardportion of the drilling machine under the influence of a hydraulic fluidacting on the back surface of the pistons.

In hydraulic percussion drilling machines presently in use, thepercussion device fitted in the frame is intended to apply successiveaxial impacts on a shank attached to a drill rod. The shank is mountedrotatably and axially slideably to the frame e.g. by a frame bushingwhich is in engagement with a rotation mechanism supported by the frame.The frame in turn is secured to a feed carriage on which the drillingmachine is displaced along the feed rail of the drilling equipment.

On drilling a rock, an impact impulse is reflected from the rock to thedrilling machine, and the force caused by the impulse has to be receivedin the drilling machine somehow. For this purpose, various flexibleaxial bearing arrangements have been developed for drilling machines toprotect them against reflected impact-like stress impulses. Sucharrangements include those disclosed in FI Patent Specification 58816,DE Auslegeschrift 2 738 956, SE Published Specification 440 873 and DEOffenlegungsschrift 2 610 619.

These flexible axial bearing arrangements known from the prior art havethe drawback of being complicated, in addition to which they require agreat number of seals and enable no adjustment of flexibility, that is,the rigidity of the axial bearings is invariable. A further drawback isthat the flexing phenomenon occurs with a delay and depends on the feedpower applied to the drilling machine.

FI Patent Application 861851 discloses an arrangement in which the axialbearing comprises several pistons positioned radially around the shank,whereby the pressure of a hydraulic fluid acts on one end of the pistonsso that the pistons adjust the position of the shank within apredetermined area. In certain cases, however, it is necessary that thepercussion point of the shank can be determined precisely in eachparticular case while maintaining the flexibility of the axial bearing,which cannot be fully accomplished with this arrangement.

The object of the present invention is to provide an arrangement for anaxial bearing in a drilling machine which avoids the drawbacks of theprior art described above. This is achieved by means of an arrangementof the invention, which is characterized in that the length of travel ofsome of the pistons towards the forward portion of the drilling machineis limited so that when they are in their foremost position and theshank is supported by the pistons, the percussion surface of the shankis positioned substantially at its optimal percussion point, whereby thepressure of the hydraulic fluid acting on the back surface of thepistons at least during the drilling is arranged to be such that thetotal force exerted on the shank by all the pistons so as to force itforwards exceeds the feed force acting on the drilling machine duringdrilling.

An advantage of the arrangement of the invention is that when thepressure of the hydraulic fluid causes the pistons to travel forwards,some of the pistons stop in their foremost position, so that the shankis always positioned at its optimal percussion point when it issupported by the pistons. After the impact, however, some of the pistonsare able to follow the shank during the percussion movement so that theydeaden the return movement of the shank before it reaches the percussionpoint during the return impulse. When the shank reaches the percussionpoint, all the pistons deaden the return impulse efficiently. Whenever anew impact is to be made, the shank is always at the percussion point,since the force acting on the pistons is altogether greater than thefeed force, whereas the feed force exceeds the total force produced bythe pistons capable of following the shank after the movement of thepistons having their stroke length limited to the percussion point hasstopped. A further advantage of the invention is that it is simple tomanufacture and the pistons of different stroke length are very simpleto construct and hence economical to manufacture.

In the following the invention will be described in greater detail bymeans of certain preferred embodiments shown in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the principal features of a drilling machineprovided with an axial bearing arrangement of the invention;

FIG. 2 is a sectional view taken along the arrows II--II of FIG. 1;

FIG. 3 shows the arrangement of the invention on a larger scale;

FIG. 4 illustrates the arrangement of FIG. 3 after an impact made by apercussion piston;

FIG. 5 illustrates the arrangements of FIGS. 3 and 4 at the initialstage of the return impulse of the shank;

FIG. 6 illustrates the arrangement of FIGS. 3 and 4 at the final stageof the return impulse;

FIG. 7 illustrates another embodiment in which the back portion of thepistons is provided with a throttle means for increasing the reflectioneffect either continuously during the return movement or when the returnmovement extends farther back than usual; and

FIG. 8 is a side view of one embodiment of a limiter.

DETAILED DESCRIPTION OF THE DRAWINGS

In the example of FIG. 1, a percussion piston 1 moves within a frame 6formed by a number of components in a manner known per se. A shank 2 issecured to the frame by means of a rotatable and axially movable framebushing 3. A separate hydraulic motor M imparts a rotational movement tothe shank 2 through a gear transmission T. The hydraulic motor and thegear transmission, which are known per se, are shown schematically inFIG. 1. The outer periphery of the frame bushing 3 is provided withteeth which are engageable with the above-mentioned gear. The innersurface of the frame bushing 3 is provided with an engaging gearingwhich is axially movable with respect to the gearing of the shank. Theframe bushing 3 is journalled radially along its outer periphery to theframe 6 at its both ends.

These matters are known per se to one skilled in the art, so theirdetails or operation require no further discussion herein.

For receiving impact impulses reflecting from the rock to the drillingmachine, the frame 6 is provided with an axial pressure bearing which ismade flexible by arranging it to move axially under the influence of ahydraulic fluid acting on it. The axial bearing is formed by severalpistons 4a, 4b which are fitted in axial housings provided in the framealong a periphery circumscribing the shank 2 and which areinterconnected with a conduit system 7. This structure appearsparticularly clearly from FIG. 2.

As can be seen from FIG. 1, the conduit system 7 is arranged to open tothe bottom of each housing behind the piston fitted in the housing asviewed in the direction of feed of the drilling machine. The conduitsystem 7 is formed by a ring-shaped conduit 7a, conduits 7b leading fromthe conduit 7a to the housings, and an inlet and outlet conduit 7c and7d, respectively. In the example of FIG. 1, a throttle means 12adjusting the flow of lubricant to the gear part of the shank is fittedin the outlet conduit 7d. Hydraulic components adjusting the flow andpressure of the hydraulic fluid in the conduit system 7 of the axialbearing are connected to the inlet conduit 7c. These components will bedescribed below.

The forward travel of the pistons 4a, 4b of the axial bearing is limitedby a limiter ring 5 provided in the frame 6. The inner periphery of thelimiter ring 5 is smaller than the periphery of an envelope drawn aroundthe outer edges of the pistons 4a, 4b. The backward travel of eachpiston 4a, 4b is limited by the bottom of the respective housing. Theshank 2 is supported by a separate support ring 8 provided behind it,and the backward surface of the support ring 8 bears on the forwardsurfaces of the pistons 4a, 4b. Since the pistons 4a, 4b are fitted inplace without seals, leakage of hydraulic fluid will occur, so that theescape of the fluid into the percussion space is prevented by a seal 9.The seal 9 is positioned at the backward end of the shank in the frame6. The escape of oil serving as a hydraulic fluid from the forwardportion of the frame 6 is prevented with a seal 11. As used above, theterm forward refers to movement in the direction of feed of the drillingmachine, and the term backward refers correspondingly to movementopposite to the direction of feed, etc.

The structure and lubrication of the gear portion of the frame bushing 3and the shank 2 may be such as disclosed in FI Patent Specification66459, for instance. As to the lubrication, it is merely to be mentionedherein that air is applied in front of the seal 9 to the back end of theshank 2. In FIG. 1, the blowing of air is indicated with the referenceIP. The function of the air is to convey oil to points to be lubricatedonto the bearings and to level out flow variations and to preventcavitation. Air is removed from the oil before the oil is filtered andpassed into a tank.

The axial bearing used in the embodiment of FIG. 1 is shown on a largerscale in FIGS. 3 to 8. The invention will be described below withreference to these figures.

In FIG. 3, the limited range of travel of the pistons 4a and 4b isindicated with the reference Δa and Δb, respectively. As used herein,the term limited range of travel refers to the axial range of travel ofthe piston. This range of travel is limited by the limiter ring 5 andthe bottom of the respective housing, as mentioned above. In theinvention, the range of travel of the pistons 4a and the range of travelof the pistons 4b are so limited towards the forward portion of drillingmachine that they are unequal: the limiter ring 5 comprises recesses 5ainto which the pistons 4a are able to move over a longer distancetowards the forward end of the drilling machine than the pistons 4b. InFIG. 3, the pistons 4a and the pistons 4b are in a position ΔY asmeasured from the bottom of the housing. Pressure applied to the conduitsystem 7 exerts a force on the pistons 4 so that each piston 4b bears onthe support ring 8, which in turn bears on the shank 2. This situationis illustrated in FIG. 3. As the force produced by the pressure of thehydraulic fluid acting on the pistons 4a and 4b is greater than the feedforce of the drilling machine during the drilling process, the pistons4a and 4b have moved forwards so far that the pistons 4b bear on anabutment surface on the limiter ring 5. The percussion surface of theshank 2 and hence the shank are at an optimal percussion point in viewof the transmission of the impact power and is not able to move fartheras the force acting on the shank through the pistons 4a is smaller thanthe feed force acting on the drilling machine due to the prevention ofthe travel of the pistons 4b, so that this force is not able to forcethe shank forwards beyond the percussion point. After the shank 2 hasmoved backwards up to the percussion point, the pistons 4b having themore limited range of travel receive the support ring 8 of the shank,and when the shank further moves backwards under the influence of thereturn impulse, the combined force of the pistons 4a and 4b deadens thereturn movement, which rapidly stops the return impulse.

The impact of the percussion piston 1 on the end of the shank 2 causes arapid steplike displacement ΔZ of the shank. This situation isillustrated in FIG. 4.

After this situation, the pistons 4a displace the support ring 8 so thatit follows rapidly the movement of the shank 2 in such a way that it isagain pressed against the shank 2. This situation is illustrated in FIG.5.

After the impact produced by the percussion piston 1, the stress impulsereflecting from the rock causes a rapid steplike displacement of theshank 2, though in a direction opposite to that described above. Onreceiving the reflected impulse, the support ring 5 is, however, in theposition shown in FIG. 5, so that the axial movement of the shank 2 isreceived by the flexible pistons 4a of the axial bearing. The pistons 4adeaden the backward movement of the shank until the back surface of thesupport ring 8 strikes on the front surface of the pistons 4b having themore limited range of travel, whereafter both the pistons 4a and thepistons 4b limit the movement of the shank as shown in FIG. 6. Since thepistons 4a and 4b and the support ring 8 follow the movements of theshank nearly without delay, the reflection impulse acting on the shank 2can be received by the pistons of the axial bearing irrespective of thedelay in the entry of the reflection impulse. Thereafter the pistons 4aand 4b again force the shank back to the percussion point-for a newimpact, as shown in FIG. 3.

FIG. 1 shows one preferred hydraulic connection, by means of which theabove operation can be accomplished. A hydraulic liquid used as apressure fluid is introduced by means of a pump 20 through a conduit 17to the inlet conduit 7a through the throttle means 13. The desiredoperation is achieved by adjusting the pressure of the system to asuitable level by means of a pressure regulation valve 15. The speed ofthe pistons 4a and 4b is accomplished by a pressure accumulator 14 whichpressurizes the conduit system 7 while the throttle means 13 reduces theflow of liquid in the direction towards the pump 20.

In the arrangement shown in FIG. 7, a bar-like projection 16 extendinginto a recess 17 formed in the conduit 7b is provided in the backsurface of the piston 4b. A gap remaining between the projection 16 andthe recess 17 serves as a throttle for liquid escaping from behind thepiston 4b and correspondingly throttles the flow of liquid behind thepiston to some extent when the piston travels forwards. The propertiesand possible progressiveness of the throttle can be affected by varyingthe length and shape of the projection 16. In the same way it can bedetermined at which point along the path of the piston the throttlebegins to act. The projection can be shaped so that it tapers away fromthe piston 4b, so that the gap is larger at first and decreases as thepiston 4b moves backwards, simultaneously increasing the effect of thethrottle.

The piston 4a in turn comprises a short pinlike projection 18, acorresponding recess 19 being provided in alignment with the projection18 at the inlet end of the conduit 7b. The recess is so dimensioned thata narrowish gap remains between the projection 18 and the recess 19.When the projection 18 reaches the edge of the recess 19, the flow ofliquid begins to throttle, so that the striking of the piston 4a on thebottom of its recess is at least retarded and in most cases preventeddue to the throttle effect.

The throttle means of FIG. 7 are possible alternatives but they can bemodified in various ways. All the pistons can be provided with throttleswhich can be similar or dissimilar depending on the type of the piston.Furthermore, it is possible that only some of the pistons are providedwith throttles, and different types of throttles can be used dependingon the properties of the drilling machine.

FIG. 8 is a side view of the limiter ring 5, in which a recess 5a isformed at every other piston 4a, for instance, in such a way that thepiston 4a is able to move farther onwards than the piston 4b in theaxial direction of the limiter ring 5 and thus in the axial direction ofthe drilling machine. For purposes of clarity, FIG. 8 shows only onepiston 4a and one piston 4b. FIG. 8 illustrates a situation in whichboth pistons 4a and 4b have travelled so far forwards in the axialdirection of the drilling machine as is possible for them. The piston 4bis thereby supported on the upper edge of the limiter ring 5 and thepiston 4a on the bottom of the recess 5a, the upper edge and the bottomthus acting as abutment surfaces. As a consequence, the pistons arepositioned at different heights in the axial direction.

The embodiments described above are by no means intended to restrict theinvention but the invention can be modified within the scope of theclaims in various ways. Accordingly, it is obvious that the invention orits parts need not be exactly similar to those shown in the drawings,but other solutions are possible as well. The housings accommodating thepistons can be made in any appropriate way, e.g., by drilling cylindersof suitable size within the frame. Correspondingly, the pistons can beformed by straight cylinder pins, etc.; and they need not be such asshown in the figures but pistons of other shape can also be used.Further, even though the drawings and the description related to themare concerned with an arrangement in which the pistons are divided intotwo groups so that some pistons are able to move towards the forward endof the drilling machine only to such an extent as is required forbringing the drilling machine to the percussion position, while theothers are able to travel forwards therefrom e.g. substantially over thelength of travel of the shank, it is equally possible to divide thepistons into more than two groups, so that one piston group travels partof the distance relative to the percussion point, and the rest travel adistance equal to that described in the above examples, that is, a stilllonger distance, whereby the return movement of the shank is deadened ina stepwise manner when the different piston groups are connected inoperation one after the other. The hydraulic system used for adjustingthe axial bearing may be connected in series with the lubrication systemof the gear part of the shank, as shown in the figures; this, however,is not the only alternative but the adjustment system of the axialbearing and the lubrication system of the gear part of the shank can bemade separate from each other, if this is regarded as necessary.

I claim:
 1. An arrangement for an axial bearing in a drilling machinecomprising a frame (6); a percussion device (1) fitted in the frame; ashank (2) positioned on an axial extension of the percussion device andhaving a percussion surface adapted to be struck by said percussiondevice; means for rotating the shank (2); and an axial bearing fitted inthe frame to receive axial forces acting on the frame (6) through theshank (2), the axial bearing being formed by a plurality of pistons (4a,4b) accommodated in axial housings formed in the frame (6) along aperiphery circumscribing the shank (2) and interconnected with a conduitsystem (7), the pistons being further arranged to travel an axialdistance axially so as to act on the shank (2) to force the shanktowards a forward portion of the drilling machine under the influence ofa hydraulic fluid acting on respective back surfaces of the pistons; andmeans for limiting the axial travel distance of a first group of saidplurality of pistons towards the forward portion of the drilling machinerelative to the axial travel distance of a second group of saidplurality of pistons so that when said plurality of pistons are in aforemost position and the shank (2) is supported by said plurality ofpistons (4a4b), the percussion surface of the shank is positionedsubstantially at its optimal percussion point, whereby the pressure ofthe hydraulic fluid acting on the back surface of the pistons (4a, 4b)at least during the drilling is arranged to be such that the total forceexerted on the shank (2) by said plurality of pistons so as to force itforwards exceeds the feed force acting on the drilling machine duringdrilling.
 2. An arrangement according to claim 1, wherein the axialtravel distance of said first group of pistons from said optimalpercussion point position of the shank (2) towards the forward portionof the drilling machine is substantially equal to an axial traveldistance of the shank (2) from said optimal percussion point towards theforward portion the drilling machine, the first group of pistons (4a)being arranged to substantially follow axial movement of the shank (2).3. An arrangement according to claim 1, wherein the axial traveldistance of said second group of pistons from said optimal percussionpoint position of the shank (2) towards the forward portion of thedrilling machine is limited so that it is shorter than a length oftravel of the shank (2) towards the forward portion of the drillingmachine.
 4. An arrangement according to claim 1, and further comprisinga support ring (8) between said plurality of pistons (4a, 4b) and theshank (2), a back surface of the support ring (8) being in contact withthe front surface of said plurality of pistons (4a, 4b) and a frontsurface of the support ring (8) being in contact with a support surfaceon the shank.
 5. An arrangement according to claim 1, wherein said meanscomprises a limiter ring (5) having limiter surfaces facing towards arearward portion of the drilling machine, the limiter surface limitingthe travel of said plurality of pistons (4a, 4b) towards the forwardportion of the drilling machine when front surfaces of said plurality ofpistons strike said limiter surfaces, and wherein said limiter surfacesinclude axially spaced surfaces at least at two points so that when saidsecond group of pistons bears on their respective limiter surfaces andthe shank (2) bears on said plurality of pistons (4a, 4b), the shank (2)is substantially at said optimal percussion point.
 6. An arrangementaccording to claim 1, wherein at least some of said plurality of pistons(4a, 4b) in said first and second groups of pistons are provided at backsurfaces thereof with projections (16, 18), a corresponding recess (17,19) being formed in a hydraulic fluid conduit (7b) leading to thehousing of the piston (4a, 4b) so that a gap remains between theprojection (16, 18) and the recess (17, 19) for the flow of thehydraulic fluid, the projection (16, 18) and the corresponding recess(17, 19) forming a throttle means limiting the flow of the hydraulicfluid.
 7. An arrangement according to claim 6, wherein the projections(18) on the back surfaces of said second group of pistons are shorterthan the length of travel of the respective pistons (4a), theprojections (18) being inserted into corresponding recesses (19) whenthe respective pistons (4a) travel towards a rearward portion of thedrilling machine and rearwardly of said percussion point of the shank(2).
 8. An arrangement according to claim 6, wherein projections in backsurfaces of a second group of pistons are at least equal in length tothe travel of said second group of pistons (4b), ends of saidprojections (16) being always in corresponding recesses (17), thusforming a continuously operated throttle means between the housing ofsaid second group of pistons (4b) and the conduit (7b) for hydraulicfluid.